private IP address spaces

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Every network interface that is connected directly to the Internet must have an IP address registered with the Internet Assigned Numbers Authority (IANA), which prevents IP address conflicts between devices. If you are configuring a private network that is not connected to the Internet or one that exists behind a firewall or proxy server, you can configure devices on your network with private addresses and have only the public address configured on the interface that is visible to the Internet.

Each address class configured has a range of private addresses available for general use:

Class A: 10.0.0.0 through 10.255.255.255

Class B: 172.16.0.0 through 172.31.255.255

Class C: 192.168.0.0 through 192.168.255.255



Class A: 1.0.0.1 through 126.255.255.254

Class B: 172.16.0.0 through 172.255.255.254

Class C: 192.168.0.0 through 192.168.254.254

Class D (Reserved for Multicasting Groups): 224.0.0.0 through 239.255.255.255

Class E (Reserved): 240.0.0.0 through 254.255.255.254

Class
 Network ID
 Range of First Octet
 Number of Available Network Segments
 Number of Available Hosts
 Subnet Mask
 Leading Bits
A
 W.0.0.0
 1-126
 126
 16,777,214
 255.0.0.0
 0
B
 W.X.0.0
 128-191
 16,384
 65,534
 255.255.0.0
 10
C
 W.X.Y.0
 192-223
 2,097,152
 254
 255.255.255.0
 110
D (multicasting)
 N/A
 224-239
 N/A
 N/A
 N/A
 1110
E (reserved)
 W.X.Y.Z
 240-255
 N/A
 N/A
 N/A
 1111